Just updated Aperture to 3.1.3 and iTunes gets stuck when synching Aperture photos to my iPhone 4. I was getting the message iTunes could not sync due to missing file. I called Apple support and the rep asked me what Aperture was and wanted me to import all my photos from Aperture into iPhoto. NOOOOTTTTTTTTT! If anyone else has this issue, here is the fix. This happened to me before when I updated Aperture.
1. Make sure Aperture, iTunes and iPhoto are closed. Use cmd-Q to terminate them if theyre still open.
2. Open Finder
3. Navigate to your Home -> Pictures folder
4. Right-click the Aperture Library.aplibrary folder and select Show Package Contents
5. You should see a folder named iPod Photo Cache
6. Delete this folder
7. Start iTunes
8. Re-enable photo synchronisation in the photo sync tab
9. Click Sync Photos in the dialog that pops up
10. Choose Aperture to sync sync photos from
11. iTunes will say that your iPhone is synced to another photo library. Click yes to overwrite the old settings in iPhone.
1. Make sure Aperture, iTunes and iPhoto are closed. Use cmd-Q to terminate them if theyre still open.
2. Open Finder
3. Navigate to your Home -> Pictures folder
4. Right-click the Aperture Library.aplibrary folder and select Show Package Contents
5. You should see a folder named iPod Photo Cache
6. Delete this folder
7. Start iTunes
8. Re-enable photo synchronisation in the photo sync tab
9. Click Sync Photos in the dialog that pops up
10. Choose Aperture to sync sync photos from
11. iTunes will say that your iPhone is synced to another photo library. Click yes to overwrite the old settings in iPhone.